code: def unit_ball_L2(shape):
      """A tensorflow variable tranfomed to be constrained in a L2 unit ball.
  
      EXPERIMENTAL: Do not use for adverserial examples if you need to be confident
      they are strong attacks. We are not yet confident in this code.
      """
      x = tf.Variable(tf.zeros(shape))
      return constrain_L2(x)
  
file_path: lucid/lucid/optvis/param/unit_balls.py
imports: import tensorflow
  from lucid.misc.gradient_override import use_gradient
label_desc: Use image node_id 4 for calling a global function with example usage: unit_ball_L2(shape) and returns: constrain_L2